Circuit-switched network architectures, such as those based on synchronous optical network (SONET) or synchronous digital hierarchy (SDH) standards, were originally designed to support voice traffic using dedicated fixed-bandwidth connections. Although such networks are advantageous in that they incorporate substantial reliability and protection mechanisms, their primary disadvantage has been a lack of bandwidth efficiency.
Packet-switched network architectures, which include those based on asynchronous transfer mode (ATM) or Internet protocol (IP) standards, have traditionally been much better able than circuit-switched architectures to handle data traffic. Since data traffic is inherently bursty, it leads to underutilization of the fixed-bandwidth connections of conventional circuit-switched networks. Packet-switched network architectures provide the benefits of statistical multiplexing, which allows for better handling of bursty data traffic.
Recently, virtual concatenation (VC) and link capacity adjustment scheme (LCAS) protocols have been developed which allow more efficient use of the existing fixed-bandwidth connections associated with circuit-switched SONET/SDH network infrastructure. For example, these protocols are utilized in transmission of Ethernet over SONET (EoS) data traffic over metropolitan networks, and in numerous other data transmission applications. The VC and LCAS protocols are described in greater detail in, for example, ITU-T standards documents G.707 and G.7042, respectively, both of which are incorporated by reference herein.
Virtual concatenation generally allows a given source node of a network to form a virtually-concatenated group (VCG) which includes multiple members each associated with a corresponding data stream. The different data streams may then be transmitted over diverse routes through the network from the source node to a given destination node. The destination node recombines the streams to reconstruct the original VCG.
The LCAS protocol enhances the basic virtual concatenation functionality described above by allowing so-called “hitless” addition and deletion of members from a VCG, that is, addition and deletion of members without the introduction of errors into the transmitted data. The LCAS protocol also enables a VCG to operate at a reduced capacity after the failure of routes associated with one or more members, by allowing the temporary removal of members associated with failed routes from the VCG.
The above-cited U.S. patent applications Ser. No. 10/446,220 and Ser. No. 10/745,881 provide additional performance improvements beyond those associated with the conventional VC and LCAS protocols.
When implementing VC or LCAS related techniques, it is often necessary to provide compensation for differential delays of the diverse routes over which the various members of a VCG are transmitted. Unfortunately, providing such a capability in conventional practice typically requires that each network node be configured to include an expensive, high-speed differential delay memory. Since a given destination node may receive different diversely-routed members at different times, the differential delay memory is used to store member data until all members are received and the original data stream can be properly reconstructed.
Additional details regarding conventional aspects of differential delay compensation can be found in, for example, G. Garg et al., “Managing Differential Delay in SONET Architectures,” EE Times, January 2002, which is incorporated by reference herein.
The above-cited U.S. patent application Ser. No.10/856,444 provides improved route determination techniques for virtually-concatenated data traffic, which are capable of providing desired levels of differential delay compensation in situations in which differential delay memories are incorporated into only a subset of the network nodes.
In provisioning a set of diverse routes for members of a VCG, it is important to have an accurate estimation of link delays. For example, link delay determination is essential for proper implementation of Quality of Service (QoS) in delay-sensitive applications such as voice transmission. A given provisioned VCG circuit with a non-zero differential delay will require the destination node to hold the faster arriving members in memory until the slower ones arrive. Holding these members consumes differential delay buffer space at the sink node. Since many network nodes have only a small amount of buffer memory, the onus is on the routing algorithm to ensure that the VCG circuit is not set up along routes where members will experience more differential delay than can be accommodated by the corresponding nodes. Accurate and efficient link delay determination can therefore facilitate the provisioning of diverse routes for VCG members.
The above-cited U.S. patent application Ser. No. 10/853,422 provides link delay determination techniques which utilize virtual concatenation to determine link delay. For example, link delay may be determined in a network comprising a plurality of nodes by identifying pairs of nodes associated with a given link, and, for each of the identified pairs, setting up a VCG between the nodes of that pair. The VCGs are then utilized to make delay measurements, and the delay measurements are processed to determine delay of the given link. Such delay measurements can considerably facilitate the operation of routing algorithms in the VCG provisioning context.
Despite the important advances provided by the techniques described in U.S. patent applications Ser. No. 10/853,422 and Ser. No. 10/856,444, a need remains for further improvements, particularly in terms of routing algorithms which can take differential delay constraints into account when determining routes for VCG members.